Can you give more detail? What do you mean by a 'list', do you mean an array? I assume 'to have an item selected' means selected by the user, on-screen? What are the 'items'?
If you have a long list of Text items in an array, and you want to populate another array with a subset of the large array, you can delete the items (in an Action) then export that to a JSON file and then re-import it into the other arrays (or edit them offline into sub-files). Depends on what you want. There might be a more advanced way I don't know of.